This invention relates in general to the protection of electrical and telephone equipment from damage caused by excessive voltage surges. More particularly, the invention deals with a surge detector which protects entire electrical and telephone circuits from both ordinary surges and extreme voltage surges such as those caused by a direct lightning strike.
Surge protector and surge arrestors have long been used for the protection of electrical equipment from the erratic power surges or spikes that occur from time to time in electrical distribution systems. Each surge protector typically serves one electrical device which is deemed to be particularly important to protect, usually because of its expense or the severe problems that can result from the equipment being taken out of service. Ordinarily, the surge protector is wired in series with a fuse or circuit breaker and acts to absorb voltage spikes in order to prevent them from possibly damaging the equipment served by the protective device. The fuse of circuit breaker is relied upon to protect both the surge protector and the electrical equipment from overloads and other extreme conditions.
There are numerous problems with this conventional approach to the handling of voltage surges. Perhaps most importantly, it is recognized that conventional surge protectors are unable to effectively handle extreme transient voltage conditions such as those caused by a direct lightning strike to the power lines. Voltage of this magnitude are applied to the electrical equipment before the fuse or circuit breaker can operate to open the circuit, and destruction and other extreme damage to the equipment can result. Even in situations where the surge protector is effective, it is able to protect only the single appliance which it serves, and other appliances and the electrical system in general remain unprotected
It is thus apparent that there is a need for an electrical surge protector which acts to protect entire electrical systems and telephone systems and all appliances they serve from ordinary voltage spikes and also from the destructive effects caused by extreme transient conditions such as the surge voltages resulting from direct lightning hits. It is the primary goal of our invention to meet that need. To our knowledge, there have been no surge protectors available in the past capable of handling extreme voltage conditions, and there have likewise been no surge protectors available for the protection of the entire power or telephone systems of a residence, small business or light commercial establishment.
In accordance with our invention, metal oxide varistors serve to protect electrical systems and telephone circuits from voltage surges. The varistors are housed in a rigid polymeric shell which is mounted within the fire rated fuse box or circuit breaker box already present in the building served by the surge protector. The varistors are connected with the incoming power lines or telephone lines on the user side of the main circuit breakers or fuses. Connection of the surge protector with the electrical or telephone system is simple, and all connections are located within the enclosed fuse box or circuit breaker box.
The varistors are nonconductive when normal voltages are applied to the electrical or telephone circuit to provide power to the downline electrical or telephone equipment. However, when voltage spikes occur at levels above normal voltage levels, the varistors become immediately conductive and establish short circuits which divert the spikes from the downline equipment. In the event of extreme voltage levels such as those caused by lightning striking the power or telephone lines, the varistors accept all of the incoming power in the short circuit mode in order to protect the downline equipment long enough to permit the fuse or circuit breaker to open the circuit. The application of extreme voltages to the varistors causes them to fail sacrificially but only after they have functioned long enough to open the fuse or circuit breaker in order to protect the electrical or telephone equipment from destructive effects of the extreme voltage. The construction of the shell and the embedding of the varistors and related components in a pliable, nonflammable filler material within the shell minimizes the potential hazards resulting from catastrophic failure of the surge protector in extreme conditions.